The experiments reported here describe mechanisms of cell fate specification in the embryo of the snail Ilyanassa obsoleta. During early cleavage, the animal-vegetal axis of the embryo is subdivided by a stereotyped series of asymmetric cell divisions that produce sets of cells with similar cleavage patterns and developmental fates. Here I show that, during these cell divisions, mRNAs for multiple patterning genes co-localize with particular centrosomes and are partitioned into specific cells during cleavage. The movement of the mRNAs to the centrosomes requires the microtubule cytoskeleton, and the subsequent movement, from the centrosome to a region on the cortex, requires actin filaments. These events localize different mRNAs to distinct sets of cells with similar developmental fates. In experimentally produced cells with two interphase centrosomes, mRNAs accumulate on the appropriate centrosome, indicating that the patterned accumulation of mRNAs is controlled at the level of individual centrosomes. In a second phase of cell fate specification, one cell in the embryo (called 3D) induces several ectodermal fates in target cells. Here I show that this signaling event involves two conserved cell signaling pathways, the MAPK pathway and the Dpp/BMP2&4 pathway. MAPK activation is detected first in 3D, and then in the cells that are predicted to require the signal. Ablation of 3D prevents the activation in the responding cells, and blocking MAPK activation with a specific inhibitor prevents the differentiation of the structures that require induction by 3D. My results indicate that 3D induces MAPK activation in the responding cells and that this is required for normal patterning. I examined embryos of several other molluscs and representatives of related protostome phyla and found that, in embryos with equal spiral cleavage, MAPK was activated in 3D, but not in the responding cells. The Ilyanassa ortholog of the secreted ligand Dpp (IoDpp) is expressed in the 3D macromere. Treatment of embryos with a closely related ligand (human BMP4) induces a high frequency of extra eyes in intact embryos, and rescues the lack of eyes in embryos where 3D is not specified. These results suggest that 3D specifies multiple fates by parallel Dpp and MAPK-activating signals.

Ariidae (Siluriformes), widely distributed in world tropical shelves, includes 150-200 species, one third endemic to the New World. Males practice mouthbrooding of eggs and embryos. To study the phylogeny of neotropical ariids, a morphological matrix [26 species (three outgroup, 23 ingroup), 56 characters) was used. The strict consensus tree of 12 parsimonious trees is 85 steps long. Ariidae includes two subfamilies. Galeichthyinae includes one species endemic to the eastern Pacific, Galeichthys peruvianus. Ariinae has three New World lineages. Notarius includes seven species in the western Atlantic, Colombia to southern Brasil, and seven in the eastern Pacific, Baja California to Peru. Cathorops has two lineages, a monotypic for C. dasycephalus, from eastern Pacific, and other for the rest. There are six species of Cathorops in western Atlantic and seven in eastern Pacific. The tribe Ariopsini, 24 species, is defined by two states from the otolith. The tribe is divided in two unities. The first includes Bagre, four species, and Occidentarius platypogon, endemic to the eastern Pacific. Western Atlantic Bagre are known from Massachussetts to Brasil; the eastern Pacific species go from California to Peru. The other ariopsin unity includes Ariopsis, five species, and Sciades, six species. Ariopsis ranges in western Atlantic from Massachussetts to Venezuela and in eastern Pacific from Mexico to Peru. Sciades includes five western Atlantic species, Colombia to Brasil, and one eastern Pacific species, Mexico to Peru. The freshwater genus Potamarius , four species, three from western Atlantic rivers and one from Ecuadorian rivers, is the sister taxa to Ariopsis. Genidens , four western Atlantic species, Brasil to Tierra del Fuego, is related to ariopsins. The hypothesis for Bagre produced with the morphological matrix coincides with the topology from morphometric techniques; three phylogenetic hypotheses found with molecular techniques were different. Bagre pinnimaculatus is the sister species to B. bagre, both are the most derived species; B. marinus is the most generalized species. Other transisthmian speciation events were found within the genera Notarius, Cathorops, and Ariopsis. In the New World three lineages have independently returned to freshwaters. Some New World ariid lineages show tendency to occur mainly in marine waters.

Social spiders most likely evolved from subsocial-like ancestors, species in which siblings remain together for part of their life cycle but disperse prior to mating. Understanding the ecological conditions that favor small colony sizes and periodic dispersal in subsocial species vs. large multigenerational colonies in the social species may provide insight into this evolutionary transition. The biogeography of these spiders and the ability of prey supplementation to delay dispersal in subsocial species implicate prey abundance as an important ecological factor influencing this process. I propose a conceptual framework in which environmental prey abundance determines the rate at which prey contact webs per unit web area, colony size determines web area and prey capture success, and per capita prey capture affects when spiders disperse. To further understand how prey abundance may have influenced the evolution of sociality, I have empirically explored aspects of this framework. Within the genus Anelosimyyus, I studied two social species inhabiting an Ecuadorian lowland rain forest, a subsocial species along the edge of an Ecuadorian cloud forest, and another subsocial species occupying a temperate riparian area of Arizona. In a comparative study examining relationships among sociality, prey availability, and prey capture rate across these species, the environments of social species tended to have relatively large prey and high overall prey biomass, but not the highest numbers of prey items. Relationships among colony size, web size, and prey capture within three of these populations revealed significant foraging-related costs of increasing colony size that could be offset by the availability of high prey biomass in the form of large prey items. Finally, I conducted an experiment manipulating prey capture rate in a subsocial species that resulted in higher prey levels delaying dispersal within and among colonies. This effect often led to a single, relatively large individual remaining in nests of colonies that had been provided more prey. Overall, these findings indicate that, while the availability of high prey biomass may have allowed sociality to evolve, the concentration of prey biomass into large, but not necessarily more prey may have selected for the larger, longer-lived colonies characteristic of social species.

Cooperative breeding (CB) is found in a wide diversity of avian lineages and can be explained at several levels of analysis. After a brief introduction to the theory explaining CB, I take an historical approach to examine CB evolution in the bee-eaters (Family Meropidae). Parsimony analyses of plumage color and shape characters yielded a number of phylogenetic hypotheses. The best supported phylogenies are six fully resolved trees from three analyses and a strict consensus tree from another analysis. These trees are used to examine the possible patterns of evolution in CB and how transition correspond to transitions in other ecological and behavioral traits. Bee-eaters were also studied in Thailand. Little green bee-eaters, Merops orientalis, breed cooperatively and predation pressure may be high in this species. Blue-tailed bee-eaters, M. philippinus, breed cooperatively in dense colonies and show signs of potential extra-pair copulation and intraspecific brood parasitism. Observations of the bay-headed bee-eater, M. leschenaulti, and the blue-bearded bee-eater, Nyctyornis athertoni, document CB in the former and support non-CB designation for the latter. Cooperative breeding is either primitive in bee-eaters or evolved early in the family. Reversals to non-CB occurred in one to three lineages. Transitions in breeding systems are not generally correlated with the transitions in nesting requirements, habitat utilization, migratory behavior, or diet. Evidence suggests correlated evolution between CB and both foraging mode (weak evidence) and social systems (stronger support). This study does not support any single hypothesis for the adaptive basis of CB across the family. Social system evolutionary patterns do suggest the importance of kin selection in several lineages. Lack of change in breeding systems, given diverse ecological and behavioral circumstances, means either cooperative breeding is malleable (selectively advantageous in a variety of ecological conditions) or represents phylogenetic inertia. A final analysis demonstrates that phylogenetic confidence indices fail to express the degree to which characters in a matrix are non-conflicting and congruent (for a given level of noise) and show only limited abilities to distinguish among probabilities of analyses making type II errors.

The microherpetofaunas recovered from the Kaiparowits Plateau, Utah, are described. Small reptiles and amphibians from 16 families and at least 22 genera were obtained from the Cenomanian Dakota, Turonian to Santonian Straight Cliffs, the early Campanian Wahweap, and the Campanian (Judithian) Kaiparowits Formations. A new genus and species of polyglyphanodontine, Manangyasaurus saueri, is described. The function of the unusual teeth of polyglyphanodontines is uncertain, but may have been related to frugivory. The polyglyphanodontines, in the restricted sense, appear to be confined to the western localities of the "southern communities" in the Judithian and Lancian. The early occurrence (Turonian) of Paraglyphanodon in the Straight Cliffs Formation suggests that the polyglyphanodontines may have been widespread during earlier Ages, permitting their dispersal to or from Asia. The genus Albanerpeton is best considered a member of the Order Caudata and its provisional assignment to the Family Prosirenidae is reasonable. The Polyglyphanodontidae, as presently defined, consists of a holophyletic group consisting of Polyglyphanodon, Paraglyphanodon, Manangyasaurus, and Cherminsaurus, and a poorly defined group consisting of the Asian "Macrocephalosauridae" Peneteius may also be a polyglyphanodontine, as the subfamily is presently defined.

The evolution of wing morphology in three clades of Drosophila was investigated using a method of mapping a complex of continuous characters developed for landmark configurations. In the melanogaster subgroup, a rate test for morphological characters was applied using the mutation-drift equilibrium (MDE) model under a range of evolutionary scenarios. The results indicate that wing morphology has evolved at a slower rate than genital morphology. The rate test under the MDE model suggested that genital morphology has evolved at a neutral rate while wing morghology has been under stabilizing selection. In the cactophilic species of the repleta group endemic to the Sonoran desert, wings have evolved in response to two factors: adaptation to the density of rots in the host cacti and adaptation to Sonoran desert conditions. Aerodynamic parameters of the wing were calculated based on a steady-state aerodynamic model. Flies using larger host cacti tend to have wings of greater aspect ratio which are better suited for long range dispersal. Flies adapted to Sonoran desert conditions tend to have wings with broader bases and narrower tips, suggesting greater efficiency at fast forward flight. The evolution of wing pigmentation patterns in the Hawaiian picture-winged Drosophila was examined in a phylogenetic context. Four specific hypotheses were tested: (1) has the overall degree of pigmentation evolved from more lightly to more heavily pigmented wings; (2) has the evolution of pigmentation patterns proceeded through a process of elaboration resulting in patterns of greater complexity; (3) are the fundamental symmetries in pigmentation pattern the same for all species in this group; and (4) are the patterns of symmetry related to what is known about wing development in Drosophila melanogaster? The pattern of evolutionary changes in the level of pigmentation was not consistent with a hypothesis of gradual increase. Based on a measure of complexity derived from Shannon's information content, there is no compelling evidence to support the hypothesis of evolutionary elaboration of pattern. There is evidence for one major evolutionary shift in the pattern of symmetry. A model linking fundamental symmetries in pigmentation pattern to wing development is presented.

How might an individual's ability to learn environmental information affect competitive interactions among species? Learned behavior can influence foraging decisions. Competition for food resources can influence patterns of species coexistence via habitat selection. I wondered if both learned behavior and competition might act together to influence interactions among species. I used Rosenzweig's shared-preference isoleg theory to predict four possible ways that differences in environmental information could affect density-dependent habitat selection. To test these predictions, I conducted field experiments to examine the foraging behavior of free-living hummingbirds. I studied black-chinned (Archilochus alexandri), blue-throated (Lampornis clemenciae), and magnificent (Eugenes fulgens) hummingbirds where they coexist in the Chiricahua Mts. of Southeastern AZ. I gave hummingbirds two types of habitats (rich and poor feeders) and let them learn to associate colors with feeder quality. I confirmed that learned color associations can increase hummingbird foraging efficiency. All birds shared a preference for the rich feeders. However, they will shift their preference toward poor feeders when competitor densities are high (Pimm et al. 1985). I quantified hummingbirds' preferences for the rich feeders when both competitor densities and information (via learned color cues) varied. The data support my fourth prediction---that birds foraging with complete information enjoy reduced negative effects from competition. Without complete information, the two subordinate species (black-chinned and magnificent) shifted their preference away from rich feeders in response to high densities of the dominant species (blue-throated). Each subordinate shifted in a unique way; the black-chinned reduced its foraging efficiency, while the magnificent reduced its total foraging time. Birds foraging with complete information remained highly selective on rich feeders even with high competitor densities. Thus, learned information affected competitive interactions (for rich feeders) among these species. My results require us to consider the information-gathering (e.g., learning) abilities of individual decision-makers when we evaluate density-dependent habitat selection. These results should help us better explain patterns of species diversity and distribution, especially for cases in which species learn environmental cues. This study provides the first demonstration, either theoretically or empirically, of a link between learned behavior and its cascading effects within a guild of coexisting species.

This dissertation presents a four year field study on the movement patterns, community dynamics, and management of granivorous wintering grassland sparrows in Arizona. Chapter one focuses on within winter, local scale movement patterns. Recapture statistics and radiotelemetry both showed strong interspecific differences in movement, consistent with the idea that these species may partition niche space according to the regional coexistence mechanism. Both techniques ranked species from most to least sedentary as follows: Cassin's and Grasshopper sparrows, Baird's, Vesper, and Savannah and Brewer's sparrows. Data also indicated that fixed home range movements, and within-species constancy of movement behavior across years and study sites are generally the rule in this group. Correlations between bird abundance and summer rainfall suggest that movement may constrain large scale habitat selection processes. Chapter two presents larger scale movement data from grassland sparrows, along with a general discussion of facultative migration in birds. High between-year abundance fluctuations and low and variable rates of between-year recapture suggest that facultative migration strategies may be the rule in grassland sparrows. The use of alternative wintering sites by individual Grasshopper Sparrows provides direct evidence of limited facultative migration behavior. These patterns contrast with the largely non-facultative migration strategies that are the rule in birds. The evolution of facultative migration strategies is linked with unpredictable temporal variation in the spatial distribution of habitat conditions in the landscape. Chapter three presents three years of data on the effects of spring/summer burning and cattle grazing on wintering grassland sparrows. Vesper and Savannah sparrows responded positively to fire, while Cassin's Sparrows responded negatively. The ecologically and geographically restricted Baird's and Grasshopper sparrows utilized burned areas during the first post-bum winter and did not significantly respond to fire. Both Ammodramus sparrows also utilized the grazed pasture; they were more abundant there than in the ungrazed study area in one year. While field observations and a prior study suggest that heavy grazing can have a strong detrimental effect on Ammodramus sparrows, the results of this study suggest that moderate cattle grazing may be compatible with the conservation of these species.

I tested three models for the evolution of cooperative breeding, as applied to Harris's Hawks. The ecological constraints model argues that cooperative breeding arises in response to habitat saturation or a harsh, variable climate. I assessed group size, territory quality, and reproductive success at 45 nests during 1986 through 1990. I found that reproductive success of pairs declined when rainfall and prey declined, while reproductive success of groups remained stable, suggesting that helping is favored under harsh conditions. I found no evidence of habitat saturation. Fisherian theory suggests that parents invest more resources in individual offspring of the larger sex, i.e., the female in Harris Hawks. According to the repayment model, however, cooperative breeders preferentially invest in male offspring. Both models predict male-biased sex ratios. I sexed 87 young fledged during 1986 through 1990 and found sex ratio bias only in 1990, when all female nestlings starved. I observed feeding at seven nests with bisexual broods and found that dominant females fed female offspring more than male offspring. According to the cooperative hunting model, Harris's Hawks form groups, because groups kill larger prey, obtaining a higher per capita caloric intake. This analysis fails to consider the importance of small prey items. I compared direct observations of the prey items eaten at 41 Harris's Hawk nests with prey remains found in 18 nests and with published reports, I showed that previous reports based on prey remains were biased in favor of large prey items. Nest attendance by female birds of prey has been linked to the female's role in antipredator defense. Dominant female Harris's Hawks with helpers to assist in nest defense should therefore attend the nest less than females lacking helpers. Females rearing broods in conspicuous nests should be more attentive than females with cryptic nests. I observed nest attendance and defense at 47 nests. I found that dominant females took the leading role in antipredator defense, especially against coyotes and Turkey Vultures. Females spent more time on conspicuous nests, due to the need to shade the young from direct sunlight. Helpers had no effect on attendance.

I synthesized monitoring results for vertebrates at Organ Pipe Cactus National Monument (ORPI), 1987-1998. Small mammals, lizards, and predators were studied using ongoing Ecological Monitoring Program (EMP) protocols (trap grids; transects) and other methods (drift-fences, visual encounter, road-cruising). EMP protocols for rodents and lizards performed well, but some recalibration is needed. Populations declined to observed minima during a 1989-1990 drought, and increased with strong rains during 1990-1995. Small rodents (pocket mice) increased fastest, but declined first, after 1992. The medium-sized Merriam's kangaroo rat: increased to a 1994 peak and then also collapsed. The larger packrat increased most slowly, not declining until after 1995. These temporal differences are consistent with a tradeoff of capacity for increase with resistance to predation pressure. After post-drought increases, most lizard populations declined when predator pressure became high, after 1992, and then increased during dry years after 1995, while predators declined. Endothermic predators were monitored by simple daily record-keeping. They increased 3-4 fold from 1989-1995, with subsequent declines. A literature review showed two subguilds: a small-prey group, which increased rapidly in 1991-1993, and a larger-prey group, which increased more slowly. For most snakes, population fluctuations during 1989-1998 did not appear dramatic. Western diamondback rattlesnakes and coachwhips were the most important mammal- and reptile-eating snakes, respectively. Large cohorts of young rattlesnakes were produced during 1992 and 1993. The western diamondback approximately doubled by 1995, and the coachwhip increased during 1991-1993. I summarized results for prey taxa, using bivariate correlation and path analysis. I used precipitation as a proxy for food productivity, and constructed predation pressure indices that combined snakes and endotherms. Conspecific density was the most consistent (negative) correlate of population growth. Predation (negative) and productivity (positive) also had relatively consistent associations with annual prey population growth. Lizard population growth was positively correlated with summer rain, whereas some rodents and endothermic predators had positive correlations with winter rain. The analysis supported a competitive effect of Merriam's kangaroo rat on pocket mice. I recommend adding predator monitoring to the EMP, and propose that resource management and academic ecology may develop a beneficial collaboration in the context of monitoring programs.